Dilute Wet Granulates: Nonequilibrium Dynamics and Structure Formation

TL;DR

This paper studies the nonequilibrium dynamics of wet granular particles, revealing a phase transition from dispersed particles to large aggregates with fractal structures, driven by capillary interactions and energy dissipation.

Contribution

It introduces a model for wet granular gases showing a nonequilibrium phase transition and characterizes the evolving structure and aggregation process.

Findings

System undergoes a phase transition from fast cooling to slow cooling with aggregation.

Early cluster growth is self-similar with fractal dimension ~2.

Eventually forms a percolating, compact, but fractal cluster.

Abstract

We investigate a gas of wet granular particles, covered by a thin liquid film. The dynamic evolution is governed by two-particle interactions, which are mainly due to interfacial forces in contrast to dry granular gases. When two wet grains collide, a capillary bridge is formed and stays intact up to a certain distance of withdrawal when the bridge ruptures, dissipating a fixed amount of energy. A freely cooling system is shown to undergo a nonequillibrium dynamic phase transition from a state with mainly single particles and fast cooling to a state with growing aggregates, such that bridge rupture becomes a rare event and cooling is slow. In the early stage of cluster growth, aggregation is a self-similar process with a fractal dimension of the aggregates approximately equal to D_f ~ 2. At later times, a percolating cluster is observed which ultimately absorbs all the particles. The final cluster is compact on large length scales, but fractal with D_f ~ 2 on small length scales.